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[求助]ADV 试题一道 [推广有奖]

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mxqy 发表于 2007-7-11 12:44:00 |显示全部楼层 |坛友微信交流群

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为什么A不对?


Suppose that the Sasuser.Revenue data set has a simple index named FlightID. For which of the following programs will the index be used?

a.
proc print data=sasuser.revenue;
where flightid ne 'IA11200';
run;
b.
data someflights;
set sasuser.revenue;
where flightid > 'IA11200';
run;
c.
data someflights;
set sasuser.revenue;
if flightid > 'IA11200';
run;
d.
proc print data=sasuser.revenue;
where origin='RDU' or flightid='IA03400';
run;

Correct answer:

  1. &lt;script&gt;<br>document.write(correctAns[9])<br>&lt;/script&gt;
复制代码
b


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关键词:following programs Document Revenue sasuser 求助 试题 adv

cxu07 发表于 2007-7-11 23:15:00 |显示全部楼层 |坛友微信交流群

回复:(mxqy)[求助]ADV 试题一道

It's a confusing question.

I think, if dataset has many obs (say 100 or more, actually, Sasuser.Revenue has 142 obs, but we can't think this particular dataset, should be general, right?), using 'ne', SAS needs to process more obs then this specifical one 'IA11200' , so not effienct?

But, on the other hand, if 'IA11200' is the smallest one in the dataset, so where flightid > 'IA11200' is similar to where flightid ne 'IA11200', right? Both answer A and B are not correct? no answer for this question.

The explanation from the answer also confusing, did not mention A either:

An index can improve the efficiency with which SAS is able to access certain observations in a data set. However, an index is not always useful. SAS will not use an index to process subsetting IF statements, or other statements that SAS determines might be more efficiently processed without an index.

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